This invention relates to a device for diagnosing the charging state of a battery adapted to store the energy generated by a generator driven by the engine of a vehicle.
In a vehicle charging system of this type, a pilot lamp is connected between the initial excitation terminal and the voltage detection terminal of the voltage regulator, so that it may be determined from observation of the pilot whether or not the charging system operates satisfactorily. Since the battery is charged or discharged through electrochemical change as is well known in the art, the terminal voltage and the internal resistance thereof depends on the charging state. The charging function depends on the ambient temperature, the specific gravity and the acidity of electrolyte and the number of charge and discharge cycles to which the battery has been subjected. Thus, the battery has intricate variable factors, and accordingly it is impossible to determine the condition of the battery in detail merely from observation of the pilot lamp.